Pure C: Adapted scons configuration for enhanced detection
Pure C: Adapted scons configuration for enhanced detection

* This should make it detect gcc compiler of sufficient versions or
  fallback to g++ compiler.

* Added support for "CC" compiler enviroment variable too.

* Blacklisting scons tools that should not be found, in the hope of
  reducing bloat of scons.

* The version detection is now the one from scons.

* No longer care for clang versions, not necessary anymore.

* Change wording to inside on C compiler.

* We no longer abuse C++ sequence points, remove that compiler options.

* Might need more work for RHEL 5 with EPEL to continue to work.

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